In the formation of photographic paper it is known that the base paper has applied thereto a layer of polyolefin resin, typically polyethylene. This layer serves to provide waterproofing to the paper and provide a smooth surface on which the photosensitive layers are formed. The formation of the smooth surface is controlled by both the roughness of the chill roll where the polyolefin resin is cast, the amount of resin applied to the base paper surface and the roughness of the base paper. Since the addition of polyolefin resin to improve the surface adds significant cost to the product it would be desirable if a smoother base paper could be made to improve the gloss of the photographic paper.
Typical photographic grade cellulose paper base has a particularly objectionable roughness in the spatial frequency range of 0.30 to 6.35 .mu.m. In this spatial frequency range, a surface roughness average greater than 0.50 micrometers can be objectionable to consumers. Visual roughness greater than 0.50 micrometers in usually referred to as "orange peel". An imaging element with roughness less than 1.10 .mu.m at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm is considered smooth and is typically defined as a glossy image.
Traditional photographic papers contain chemistry to provide certain properties to the paper that are not inherent in the paper fiber. This chemistry includes materials known in the art to improve wet strength and dry strength. Since photographic paper that comprises laminated biaxially oriented polyolefin sheets laminated to base paper has greatly improved tensile strength over traditional photographic papers, the addition of wet and dry strength to the paper adds unwanted cost to the product. It would be desirable if a base paper could be made that was free of wet and dry strength resins.
It has been proposed in U.S. Pat. No. 5,866,282--Bourdelais et al., to utilize a composite support material with laminated biaxially oriented polyolefin sheets as a photographic imaging material. In U.S. Pat. No. 5,866,282, biaxially oriented polyolefin sheets are extrusion laminated to cellulose paper to create a support for silver halide imaging layers. The biaxially oriented sheets described in U.S. Pat. No. 5,866,282 have a microvoided layer in combination with coextruded layers that contain white pigments. The composite imaging support structure described in U.S. Pat. No. 5,866,282 has been found to be more durable, sharper and brighter than prior art photographic paper imaging supports that use cast melt extruded polyethylene layers coated on cellulose paper. The surface roughness of the paper base in U.S. Pat. No. 5,866,282 is replicated on the surface of the imaging element.
It has been proposed in U.S. Pat. No. 5,244,861 to utilize biaxially oriented polypropylene laminated to a base paper for use as a reflective imaging receiver for thermal dye transfer imaging. While the invention does provide an excellent material for the thermal dye transfer imaging process, this invention can not be used for imaging systems that are gelatin based such as silver halide and ink jet because of the sensitivity of the gel imaging systems to humidity. The humidity sensitivity of the gel imaging layer creates unwanted imaging element curl. One factor contributing to the imaging element curl is the ratio of base paper stiffness in the machine direction to the cross direction. Traditional photographic base papers have a machine direction to cross direction stiffness ratio, as measured by Young's modulus, of approximately 2.0. For a composite photographic material with laminated biaxially oriented polyolefin sheets to a base paper it would be desirable if the machine direction to cross direction stiffness ratio were approximately 1.6 to reduce imaging element curl.
A receiving element with cellulose paper support for use in thermal dye transfer has been proposed in U.S. Pat. No. 5,288,690 (Warner et al.). While the cellulose paper in U.S. Pat. No. 5,288,690 solved many of the problems existing with thermal dye transfer printing on a laminated cellulose paper, this cellulose paper is not suitable for a laminated cellulose photographic paper since this paper has undesirable surface roughness in the spatial frequency range of 0.30 to 6.35 mm and the pulp used in U.S. Pat. No. 5,288,690 is expensive compared to alternative pulps. It would be desirable if "orange peel" roughness could be minimized in the laminated photographic base paper.